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Thursday, July 14, 2011

Is PrEP the future of HIV prevention?

A recent sense of optimism surrounding PrEP was a result of the Chemoprophylaxis for HIV Prevention in Men study (also known as iPrEx), a Phase III clinical study — sponsored by the National Institutes of Health (NIH) through a grant to the J. David Grant Institutes at the University of California at San Francisco — that began in July 2007 and was published in the New England Journal of Medicine of November 23, 2010.

The iPrEx study focused on 2,499 sexually active men who have sex with men and transgendered women who have sex with men — all of whom were HIV-negative at the time of enrollment. The study’s experimental group received a PrEP treatment — a daily tablet that combined 200 milligrams of the drug emtricitabine, or FTC, and 300 milligrams of the drug tenofovir (a combination known by the brand name Truvada) — while the control group received a placebo.

In all, 100 cases of HIV infection occurred among participants in the iPrEx study. Thirty-six infections occurred among the 1,251 participants who were chosen to receive Truvada, while 64 occurred among the 1,248 participants who had received the placebo. Based on those numbers alone, PrEP was approximately 44 percent effective in preventing seroconversion.

While 44 percent efficacy might not be seen as wholly significant, what created perhaps a greater stir among researchers was analysis of the infected members of the experimental group. Blood tests revealed that, of the 36 men receiving PrEP who had seroconverted, 33 had no traces of the drug in their body prior to their positive HIV tests.

This data presented a startling result: if the subjects who were supposed to have been taking Truvada daily — but were apparently not — were not counted, the efficacy of PrEP treatment rose from 44 percent to more than 90 percent.